1. Field of the Invention
This invention relates to an improved method for recovering volatiles generated by a coke drum. In particular, it relates to a vacuum residuum flashdown technique for separating absorbed coke drum vapors from coker combination tower residuum.
2. Discussion of the Prior Art
Processing of crude petroleum oil to recover fractions suitable for upgrading in various refinery processing operations employs multi-stage distillation towers. Crude oil is first distilled or fractionated in an atmospheric distillation tower and further separated in a vacuum distillation tower. In this combination operation, gas (C.sub.4.sup.-) and gasoline are recovered as overhead products of the atmospheric distillation tower, heavy naphtha, kerosene and gas oils are taken off as distillate side streams and the residual material is recovered from the bottom of the atmospheric tower as reduced crude. The residual bottoms fraction is usually charged to a vacuum distillation tower. The products of vacuum distillation include vacuum gas oils and a heavy residual material known as vacuum reduced crude. The vacuum reduced crude is fed into a coker combination tower, where it quenches, and recovers heat from hot vapor from a coke drum or furnace (hereinafter coke drum). The residual crude, which is not vaporized by the heat of the vapor from the coke drum in the coker combination tower, is then fed to the coke drum as a feedstock for coke manufacture.
Typical prior art distillation techniques are disclosed in U.S. Pat. Nos. 3,501,400; 3,886,062; 4,239,618 and 4,261,814. A typical coker combination tower and coke drum is disclosed in U.S. Pat. No. 3,917,564.